Solar energy appears to be the single most attractive source of energy. Solar systems are not liable to wind damage, as is the case with wind energy systems. They can be installed almost anywhere, unlike tidal energy which must be located in coastal areas. Solar energy systems consume no fuel and the energy is, therefore, fuel and is, therefore, "free", in a sense. It causes no emissions to pollute the environment. It does not appear to require complex transmission and delivery systems such as electrical power lines, gas or oil pipe lines, or other delivery systems, provided it can be collected "on site", i.e., where it is to be used.
Solar energy has however one major disadvantage, namely, that it is available only intermittently, in the hours of daylight. Accordingly, it is obvious that sufficient solar energy must be collected during the hours of daylight, that a sufficient quantity of energy can be stored, for reuse during the hours of darkness when it is not available. Clearly, systems could be engineered to carry out these functions on a very large scale. However, that would then require the collection and storage of large quantities of solar energy which would then have to be transmitted from place to place, for example, to a large number of homes, connected to a central solar collector. This would result in excessive capital costs, and would likely result in relatively high energy transmission losses. Clearly, such centralized systems would fail to take advantage of the principal significant fact concerning solar energy, namely, in that it is substantially universally available over a large portion of the face of the earth, and thus does not require special transmission systems, to transmit the energy from one place to another. The theoretically ideal solar energy system would be self-contained, so that individual systems could be provided for individual buildings or homes, so that each building or home could be essentially energy self-sufficient. In this way, complex transmission or generation systems would not be required.
It is however apparent that in the design of any solar energy collector system it will be necessary to collect solar energy falling on a relatively substantial surface area, to provide sufficient energy even for a single home or building. In order to achieve this, numerous proposals have been made for providing solar collectors based on some form of concave curved mirror usually of parabolic shape having a relatively large surface area. The mirror catches the sun's rays falling on all points of the mirror, and concentrates them into a single point, resulting in a high energy concentration of light at that point. Usually, at the focal point of the mirror, a secondary reflector is provided for reflecting the concentrated point of light, and redirecting it, so as to convert the energy of the concentrated light beam into some other form of energy. Typical proposals of this general type are shown in, for example, U.S. Pat. Nos. 4,286,581, 4,295,462, 4,340,031, and 4,696,285. It is, of course, implicit in any of these solar collector devices that the actual mirror itself must be located in the open air. In all of these proposals, the mirror concentrates the solar energy falling on the mirror at the focal point of the mirror. The concentrated light is re-directed into a portion of the collector where the energy of the light beam is then converted into heat. For example, in U.S. Pat. No. 4,286,581, the solar energy is utilized to heat a tubular chamber, or cavity, and a fluid medium is passed through the chamber or cavity, and absorbs the heat from the concentrated light rays. The energy in the fluid is then transported to some other location for use. It is, of course, implicit in any of these proposals that the mirror must be mounted on a suitable tracking mount, so that the mirror can always be pointed directly at the sun. This is a necessary and essential feature, since unless the mirror is pointed exactly at the sun, the sun's rays when reflected by the mirror will not be received on the secondary reflector and will thus not be concentrated into the light beam but will simply be reradiated into the atmosphere. Accordingly, in the proposals of the type described above, it is usually necessary for the entire apparatus consisting of the mirror, the secondary reflector, and also the heat conversion chamber, all to be mounted together and moved simultaneously to track the path of the sun. Such systems therefore require highly complex suspension and transmission mechanisms, to provide the facility for accurate tracking of the sun, by all of the the components simultaneously.
Other proposals for collecting solar energy have been made of a more simplistic nature, for example as shown in U.S. Pat. No. 4,059,226. In this type of proposal, large chambers are filled with any suitable heat storage medium. In this case, the medium is simply rock or stone. The chambers are fixed in position, and have glass panels through which the sun's rays may pass and heat up the stones. In the particular example, of this patent, insulating panels are adapted to be swung down over the glass panels, when the heat generated by the sun's rays falls below a certain preset minimum temperature.
Systems of this kind are relatively massive installations, and are suitable in only relatively limited "sun belt" portions of the globe, and must obviously be located for optimum operation in a fixed location, i.e., facing south in the Northern hemisphere.
Another proposal is shown in U.S. Pat. No. 3,988,166. In this patent, a concave mirror is provided, mounted on a suitable tracking mount, and having a secondary light concentration mirror at the focal point. The light falling from the main mirror on the secondary mirror is concentrated into a light beam. A central opening in the main mirror allows this concentrated light beam to pass through the main mirror. An energy collection chamber is provided immediately behind the main mirror, for receiving energy from the concentrated light beam. The converted energy is then transmitted from this chamber, to a location where it may be of use. While this system is somewhat simpler to construct, it still has the disadvantage that the energy conversion takes place out of doors, and requires the transmission of an energy conversion medium, typically, for example, a fluid medium, from the solar collector itself into the building or facility where the energy is required, typically to heat the building or to provide hot water for a domestic hot water system. Thus thick insulation must be provided to limit heat losses in transmission.